The nicotinic acetylcholine alpha-subunit gene tar-1 is located on the X chromosome but its coding sequence is not involved in levamisole resistance in an isolate of Trichostrongylus colubriformis.
The polymerase chain reaction was used to amplify fragments comprising the known reading frame of the nematode nicotinic acetylcholine alpha-subunit gene tar-1. Sequences were derived from DNA prepared from bulk collections of worms and from individual male and female Trichostrongylus colubriformis. In each case a levamisole-resistant (BCk) and a drug susceptible population were examined. Although several nucleotide transitions were detected no amino acid sequence variations were found between the isolates and between individual worms, indicating that the coding sequence of this gene is not responsible for levamisole-resistance in the isolate tested. However, an intronic allelic T/C variation at position 4955 was observed in both populations. It has been reported that levamisole-resistance in the BCk isolate of T. colubriformis is due to a sex-linked recessive gene or gene complex. A restriction fragment length polymorphism formed by the allelic variation was found and was detectable by digestion with the restriction endonuclease NlaIII. Statistical comparison of allele frequencies from individual male and female worms was consistent with sex-linkage of tar-1 (P < 0.05) but showed no correlation with levamisole resistance status. The polymorphism described will provide a useful X-chromosome marker and represents the first mapped genetic locus in this species.
Wiley
L J
LJ
Department of Veterinary Anatomy and Pathology, University of Sydney, NSW, Australia.
Ferrara
D R
DR
Sangster
N C
NC
Weiss
A S
AS
D000483:Alleles; D000818:Animals; D000969:Antinematodal Agents / Q000494:pharmacology*; D001483:Base Sequence; D002874:Chromosome Mapping; D004351:Drug Resistance / Q000235:genetics; D005260:Female; D017238:Genes, Helminth; D008040:Genetic Linkage; D005819:Genetic Markers; D014644:Genetic Variation; D007978:Levamisole / Q000494:pharmacology*; D008297:Male; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D011978:Receptors, Nicotinic / Q000235:genetics*; D017422:Sequence Analysis, DNA; D014254:Trichostrongylus / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D014960:X Chromosome / Q000235:genetics*
D000969:Antinematodal Agents; D005819:Genetic Markers; D011978:Receptors, Nicotinic; D007978:Levamisole